Process for the continuous preparation of acetic acid from acetaldehyde



April 3, 1934. K. wlEsLER PROCESS FOR THE CONTINUOUS PREPARATION OF ACETIC lACID FROM ACETALDEHYDE rFiled Feb. 14. 1930 420 essary, is further considerably increased.

Patented Apr. `3, 1934 PROCESS FOR TBE CONTINUOUS PREPARA- TION OF ACETIC ACID FROM ACETALDET- HYDE Karl Wiesler, Constance, Germany, assigner, by

mesne assignments, to the Vfirm of Deutsche Goldund Silber- Scheideanstalt vormals Roessler, Frankfort-on-the-Main, Germany, a corporation oi Germany Application February I4, 1930, Serial No. 428,456A- In Germany February 27, 1929 'z claims. (ci. zoo-116) It is known that in the oxidation of acetaldehyde with oxygen labile intermediate products (peracid) are formed which can give rise to explosions For obviating the difficulties resulting 6 from this it has been proposed amongst other that'the heat developed by the reaction, which `moreover renders extensive cooling methods nec- According to the present invention a continuous production of acetic acid from acetalde- Ihyde is eiected in a non-dangerous manner, in

o that the peracetic acid formed is maintained in great dilution by continuous. circulation of crude acetic acid, for example, in concentrations of less than'0.2% and in this form having a large surface, is caused to react with gaseous acetaldehyde.

It has been shown to be possible to withdraw 80' the peracid formed with further quantities oi.' aldehyde so as to' obtain a successful practical conversion free from loss without the peracid concentrations being able to increase in an appreciablemanner at any'single place of the apaparatus.

Therefore, in working according to the invention it is possible to omit the use of catalysts or heat for the purpose of destroying all other unavoidable peracids as in the hitherto usual 40 methods.

The conversion of the peracid with the acetaldehyde iseifected according to the equation `In this way no loss of aldehyde occurs, also no oxygen is used for side reactions which have the effect of a deleterious increase of the reaction heat.

When carrying out the invention, crude acid poor in peracid is continuously circulated at a certain rate. This crude acid is mixed in a certhe produced crude acid poor in peracid on realso where it is preferably formed that it can tain proportion with the acetic acid containing peracid which is freshly formed by the oxidation of acetaldehyde with air. The peracid concen. tration of the mixture is thereby reduced to the desired'low value, which is non-injurious, for example to 0.2% or less. This diluted solution of peracetic acid in crude acetic acid continues the circulation and is now caused to react with gaseous aldehyde on a large surface, preferably at relatively low temperatures, for example such between 20 and 50 C. The peracid reacts with l acetaldehyde while forming acetic acid. The peracid concentration in the circulating crude acid is thereby reduced to such an extent that peating the circulation can again be used for `diluting freshly formed acetic acid containing peracid.- In this manner, the peracid is kept in such dilution in all parts of the apparatus and never occur inquantities which could exert any detrimental eiect. In this manner, the reaction takes place between peracid and acetaldehyde, as has been found. almost exclusively according to the above equations.

The conversion of the peracid into acetic acid can, for example, be effected in towers provided with cooling devices and filled with suitable filling material. With suitable regulation of the reaction temperature it is easily possible to reduce peracid by the action of aldehyde to quite small, no longer injurious quantities, for example, a few hundredths per cent, with the formation of acetic acid, so that the now practically peracid-free crude acid is available for diluting the reaction In carrying out the invention the operation can be carried out for example in such a manner that the initial substances, namely liquid acetaldehyde and oxygen, or oxygen containing gases, for example air, are introduced into a vessel which is provided with a good acting stirring mechanism and al cooling device, and is con- The vessel temperature is preferably kept below 70 C., for example from 60 to 70 C.

The crude acid continuously flowing out from the vessel is cooled in a cooler to, for example, 15 C. and pumped up into the towers, whilst .the vapour mixture issuing from the vessel which contains the unconverted aldehyde, moderate vquantities of oxygen and very small quantities of between the undecomposed aldehyde and the oxy-l gen still present, and therefore the runnings-oi from the tower might show a higher peracid content than was desirable. The runnings-.off from the tower consisting of crude acid which only contains a few hundredths percent of peracid, is led back again into the stirring vessel and here now serves to reduce the peracid content in the vessel itself to a suitably small degree.

The invention 'also oiers the advantage amongst others that the reaction temperature in the vessel can bekept comparatively low if .only the stirring mechanism provides for a sufficiently thorough mixing of the initial substances. Whereas in other processes for the oxidation of acetaldehyde with the use of pure oxygen as oxidizing agent, in general temperatures of '70 to 100 C. are required, for the presentV process even with the use of oxygen-nitrogen mixtures, as for example air, thus under unfavourable conditions vessel temperatures of for example, 60 to '10 C. have proved to be suitable and quite suiiicient.

At such lower temperatures the side reactions already above referred to a number of times involving losses and damage by development of heat occur in a relatively small degree. Lower temperatures favour the formation of peracid. In the present case the peracid formed however, owing to the strong dilution on the one hand and the moderate'temperatures on the other hand is converted `in a large degree with the entering aldehyde tov-acetic acid, whilst the damage, for example by heat, goes entirely to the background. Thefavourable course of reaction in the vessel is amongst others obvious, from the circumstance that in spite of the dilution with the continually circulating crude acid and the strong reduction of the aldehyde concentration to, for example, only 1 to 11/%, occasioned thereby very satisfactory procedures with excellent yields are obtained, owing to the elimination of undesired side reactions.

Withwthe use' of a plurality of the described towers which serve for the conversion of the peracid, the arrangement can be carried out in various ways. It has been shown to be preferable to pass the gases, issuing from the oxidation vessel, through two of the said towers in succession. Each of these towers is sprayed with crude acid and the acid flows out of each tower directly into the oxidation vessel back again. In both towers, the reaction between peracid and acetaldehyde takes place on a large surface but the second tower acts in part as a washer for the waste gases, a part of the acetaldehyde unchanged in the gases being absorbed by the crude acid and returned to the oxidation vessel. The apparatus is then supplemented by 'a further Washing ydevicefpreferably in the form of a third tower,

in which the acetaldehyde contained in the gase is recovered in known manner.

This tower is preferably sprinkled with acetic acid whose washing action is better than that of water. Likewise, the recovery of the acetaldehyde is favourably effected by distillation of this washing agent.

It has already been proposed to use so-called reaction towers for the oxidation of acetaldehyde, eventually also with the separate method that the filling material of said towers, is previously moistened with acetic acid. The advantages of the present invention cannot be obtained with such methods of operation. If the passage of large quantities of acetic acid ceases, the dilution of the peracid to the degree necessary for safety is not possible. Furthermore a favourable running conversion with further aldehyde, with practical avoidance of loss in the form of carbon dioxide, can only be obtained with suiciently diluted peracid as is obtained according to the present invention. A favourable method of operation according to the present process arises amongst others from the fact that the carbon dioxide content in the waste gases does not further increase during the passage of the latter through the towers. i

It has also been proposed to use towers. with fillings which only leave a small space for the passage of the gases.` This method is directly dangerous as, Dwith narrow interstices it is unavoidable that at small variationscf pressure stoppages will occur which reduce the fiow of the acid or may temporarily hold it up entirely, so that the peracid concentration may assume an appreciable value locally.

Furthermore, the strong flow of acid through the tower as occurs according to the present inventionhas the further advantage that the regulation of the reaction temperature, which is of considerable importance for the efficient conversion of the peracid, is effected uniformly and reliably.

E'amples 120 1. The vessel in which the reaction takes place is provided with an inlet member for acetalde-` hyde, and for air or 'oxygen and also with a cool-l ing device and a mixing device. 45 kg. of acetaldehyde and 100 cubic meters of air are introduced continuously per hour. Thetemperature in the reaction vessel amounts to 65 C. The gas and acetaldehyde vapors which pass out are conducted into two towers arranged one behind the other, and filled with Raschig rings, both of these towers being each sprayed with the cooled crude acetic acid circulated at the rate of 250 kg. per hour. After the peracid contained therein has commenced to react with the 'rising acet- 135 aldehyde vapors at room temperature the acetic acid almost entirely free from peracid ows into the oxidation vessel. The acid flowing from the indicate the path of the gases, and the chain dotted lines the path of the acetaldehyde. From the reaction vessel A the gases pass successively through the towers I, II, III and IV, in which they are freed from the unaltered acetaldehyde. There then follows the 'washing device VI in which the acetic acid is washed. The acetic acid itself circulates through the reaction vessel A, the cooler and the receiving vessel 6 the supply vessel 1 and the towers I andvII, said reaction vessel A being provided with a water cooling coil 10. A portion, corresponding with the freshly formed acetic acid, passes from the supply vessel 1 to the supply vessel 3 and from this into the column V in which it is freed from acetaldehyde. The acetaldehyde itself is again returned to the reaction vessel A whilst the acetic acid free from acetaldehyde ows into the receiving vessel 5. From here a suitable portion is withdrawn as the finished product, whilst another portion passes to the supply vessel 2 and from here into the towers III and IV. The acetaldehyde-containing acetic acid obtained in these-towers is again passed through the receiving vessel 4 back into the vessel 3 and from here passes for distillation of the acetaldehyde into the column V.

45 kilograms of acetaldehyde areL oxidized at 45 C. per hour and by means of 100 cubic meters of air per hour. The crude acetic acid produced is circulated for spraying the towers and in the first tower at a rate of flow of 80 kilograms per hour" and in the second tower at a rate ofiiow of 270 kilograms per hour. Thereupon 300 kilograms of crude acetic acidy are circulated per hour through a distillation apparatus and thereupon freed from the dissolved acetaldehyde which is recovered in concentrated form, and then used for spraying two further towers with acetic acid freed from acetaldehyde, each at the rate of 150 kg.

taining peracetic acid issuing from the vessel,

per hour.

The gases and .vapours leaving the oxidation vessel pass in series through the four towers. The acetic acid iiowing from the iirst two towers is returned into the oxidation vessel. The acetic acid passed through the next two towers is freed continuously from acetaldehyde in a distillation column, and from the pure acetic acid thus obtherein. The acetic acid flowing from the oxida.

tion vessel contains 0.1% peracid. The yield amounts to 97% of the theoretical amount. The oxidation can be carried out for anyv suitable length of time and takes place entirely uniformly and continuously.

I claim:-

1. A process for the continuous production of acetic acid by the oxidation of acetaldehyde in liquid phase bv means of oxygen, consisting in keeping in great dilution the peracetic acid contained in crude acetic acid and formed by the reaction, by continuously circulating crude acetic acid and causing the reaction of the solution of peracetic acid in the circulating crude acetic acid issuing from the oxidation process, said reaction taking place over a large surface with vaporous acetaldehyde from said oxidation process, the temperature during the reaction being below 50 C.

A2. A process according to claim 1 in which the concentration of peracetic acid in the circulating crude acetic acid is kept below 0.2%.

3. A process according to claim 1 in which the circulating crude acetic acid amounts to a multiple of acetic acid produced by oxidation in unit time. i

4. A process according to claim 1 wherein acetic acid containing small quantities of peracid is used as the circulating crude acetic acid.

5. A process for the continuous production of acetic acid consisting in bringing acetaldehyde in liquid phase linto reaction with oxygen in a vessel, bringing the cooled, crude acid issuing from Athe reaction vessel into reaction over a large surface with the acetaldehyde-containing gas mixture issuing from the reaction vessel and returning a portion of said crude acid substantially freed from peracid to the reaction vessel.

6. A process for the production of acetic acid, consisting in bringing acetaldehyde in liquid phase into reaction with oxygen by a thorough mixing in a.' vessel,fcooling the crude acid conbringing said peracetic acid into reaction with the acetaldehyde-containing gases issuing from the reaction vessel in a tower at a. temperature below 50 C., and partly returning into the mixing vessel the crude vacetic acid thus obtained and substantially freed from peracid.

7. A process for the' production of acetic acid, consisting in bringing acetaldehyde in liquid phase into reaction with oxygen in a mixing Vessel by a thorough mixing at temperatures be'- tween 60 and 70 C., cooling the crude acid containing peracetic acid issuing from said vessel, bringing said peracetic acid into reaction over a large surface with the acetaldehyde-containing gas mixture issuing from said vessel at a temperature below 50 C., and returning into said vessel the crude acetic acid thus substantially freed from peracid. KARLWIESLER.. 

